Optical disc apparatus, focus error signal adjustment method, program, and integrated circuit

Abstract

To adjust the symmetry of a focus error signal, the symmetry of the focus error signal needs to be measured during upward and downward driving of an objective lens, which is performed at every varying setting of a signal correction gain value of the focus error signal, and such adjustment takes a long time. An optical disc device ( 100 ) measures a focus error signal before differentiation at a local maximum point and a local minimum point of a focus error signal using a prior-to-differentiation FE measurement unit ( 50 ), and calculates the symmetry of the S-shape of a focus error signal using a symmetry calculation unit ( 51 ), and performs balance adjustment based on the calculation result. The device with this structure adjusts the symmetry of a focus error signal at a high speed by requiring an upward and downward operation to be performed only once.

1 . An optical disc device that records and/or reads on an optical disc having an information surface, the device comprising:
 an illumination unit operable to emit a light beam to the optical disc;   a converging unit operable to converge the light beam emitted from the illumination unit;   a focus drive unit operable to drive the converging unit in a manner to move a spot of the light beam that has been converged by the converging unit in a direction perpendicular to a disc surface of the optical disc;   a light receiving unit including a plurality of divisional detectors, and operable to receive reflected light from the optical disc using the plurality of divisional detectors and obtain, as a positive FE signal and a negative FE signal, an electric signal corresponding to an amount of the received light;   a measurement unit operable to measure a signal level of each of the positive FE signal and the negative FE signal obtained by the light receiving unit;   a signal correction unit operable to correct the signal level of at least one of the positive FE signal and the negative FE signal by multiplying the at least one of the positive FE signal and the negative FE signal by a predetermined gain value;   a focus error signal generation unit operable to generate a focus error signal based on an output from the signal correction unit, and output the generated focus error signal; and   a signal ratio calculation unit operable to obtain, based on an output from the measurement unit, the predetermined gain value by which the at least one of the positive FE signal and the negative FE signal is to be multiplied in a manner that the predetermined gain value causes an absolute value of a local maximum value of the focus error signal to be equal to an absolute value of a local minimum value of the focus error signal,   wherein the signal correction unit corrects the signal level of the at least one of the positive FE signal and the negative FE signal based on the predetermined gain value obtained by the signal ratio calculation unit.   
   
   
       2 . The optical disc device according to  claim 1 ,
 wherein the signal ratio calculation unit obtains the predetermined gain value based on an output from the measurement unit at a point where a signal level of the focus error signal is at an extremum when the spot of the light beam is around a selected information surface of the optical disc or at a point where a signal level of each of the positive FE signal and the negative FE signal is at an extremum when the spot of the light beam is around a selected information surface of the optical disc.   
   
   
       3 . The optical disc device according to  claim 2 , further comprising:
 a focus control unit operable to control the spot of the light beam to be positioned on an information surface of the optical disc in accordance with a signal output from the focus error signal generation unit; and   a focusing unit operable to move the spot of the light beam in the direction perpendicular to the disc surface of the optical disc using the focus drive unit, and activate a control operation performed by the focus control unit when a position of the spot of the light beam agrees with a position on a selected information surface of the optical disc,   wherein the signal ratio calculation unit obtains the predetermined gain value to be used by the signal correction unit based on an output from the measurement unit at least once before the focusing unit activates the control operation performed by the focus control unit.   
   
   
       4 . The optical disc device according to  claim 2 , further comprising:
 a spherical aberration correction unit operable to correct a spherical aberration of the spot of the light beam on a selected information surface of the optical disc,   wherein the signal ratio calculation unit obtains the predetermined gain value to be used by the signal correction unit based on an output from the measurement unit after the spherical aberration is corrected by the spherical aberration correction unit.   
   
   
       5 . The optical disc device according to  claim 4 , further comprising:
 a focus control unit operable to control the spot of the light beam to be positioned on an information surface of the optical disc in accordance with a signal output from the focus error signal generation unit; and   a focusing unit operable to move the spot of the light beam in a direction perpendicular to the disc surface of the optical disc using the focus drive unit, and activate a control operation performed by the focus control unit when a position of the spot of the light beam agrees with a position on a selected information surface of the optical disc,   wherein the signal ratio calculation unit obtains the predetermined gain value to be used by the signal correction unit based on an output from the measurement unit when the spot of the light beam is moved toward the optical disc using the focusing unit, and   the focusing unit executes focus control using the focus control unit in a manner that the spot of the light beam is positioned on a selected information surface of the optical disc after the predetermined gain value is obtained by the signal ratio calculation unit.   
   
   
       6 . The optical disc device according to  claim 4 , further comprising:
 a disc determination unit operable to perform an operation of moving the spot of the light beam toward the optical disc and an operation of moving the spot of the light beam away from the optical disc using the focus drive unit to determine a type of the optical disc mounted on the device,   wherein the signal ratio calculation unit obtains the predetermined gain value to be used by the signal correction unit based on an output from the measurement unit during at least one of the operation of moving the spot of the light beam toward the optical disc and the operation of moving the spot of the light beam away from the optical disc performed by the disc determination unit.   
   
   
       7 . The optical disc device according to  claim 6 , further comprising:
 a signal ratio optimization unit operable to obtain, as a first gain value, the predetermined gain value obtained by the signal ratio calculation unit during the operation of moving the spot of the light beam toward the optical disc, and obtain, as a second gain value, the predetermined gain value obtained by the signal ratio calculation unit during the operation of moving the spot of the light beam away from the optical disc, and obtain the predetermined gain value to be used by the signal correction unit based on the first gain value and the second gain value.   
   
   
       8 . The optical disc device according to  claim 1 , wherein when the optical disc has a plurality of information surfaces,
 the signal ratio calculation unit obtains, for each of all the information surfaces, the predetermined gain value to be used by the signal correction unit based on a signal output from the measurement unit at a point where a signal level of the focus error signal is at an extremum when the spot of the light beam is around each information surface of the optical disc or at a point where a signal level of each of the positive FE signal and the negative FE signal is at an extremum when the spot of the light beam is around each information surface of the optical disc.   
   
   
       9 . The optical disc device according to  claim 8 , further comprising:
 a focus control unit operable to control the spot of the light beam to be positioned on an information surface of the optical disc in accordance with a signal output from the focus error signal generation unit; and   a focusing unit operable to move the spot of the light beam in the direction perpendicular to the disc surface of the optical disc using the focus drive unit, and activate a control operation performed by the focus control unit when a position of the spot of the light beam agrees with a position on a selected information surface of the optical disc,   wherein the signal ratio calculation unit obtains the predetermined gain value to be used by the signal correction unit based on an output from the measurement unit at least once before the focusing unit activates the control operation performed by the focus control unit.   
   
   
       10 . The optical disc device according to  claim 8 , further comprising:
 a focus control unit operable to control the spot of the light beam to be positioned on an information surface of the optical disc in accordance with a signal output from the focus error signal generation unit; and   a focusing unit operable to move the spot of the light beam in the direction perpendicular to the disc surface of the optical disc using the focus drive unit, and activate a control operation performed by the focus control unit when a position of the spot of the light beam agrees with a position on a selected information surface of the optical disc,   wherein the signal ratio calculation unit obtains the predetermined gain value to be used by the signal correction unit based on an output from the measurement unit when the spot of the light beam is moved toward the optical disc using the focusing unit, and   the focusing unit executes focus control using the focus control unit in a manner that the spot of the light beam is positioned on a selected information surface of the optical disc after the predetermined gain value is obtained by the signal ratio calculation unit.   
   
   
       11 . The optical disc device according to  claim 8 , further comprising:
 a disc determination unit operable to perform an operation of moving the spot of the light beam toward the optical disc and an operation of moving the spot of the light beam away from the optical disc using the focus drive unit to determine a type of the optical disc mounted on the optical disc device,   wherein the signal ratio calculation unit obtains the predetermined gain value to be used by the signal correction unit based on an output from the measurement unit during at least one of the operation of moving the spot of the light beam toward the optical disc and the operation of moving the spot of the light beam away from the optical disc performed by the disc determination unit.   
   
   
       12 . The optical disc device according to  claim 11 , further comprising:
 a signal ratio optimization unit operable to obtain, as a first gain value, the predetermined gain value obtained by the signal ratio calculation unit during the operation of moving the spot of the light beam toward the optical disc, and obtain, as a second gain value, the predetermined gain value obtained by the signal ratio calculation unit during the operation of moving the spot of the light beam away from the optical disc, and obtain the predetermined gain value to be used by the signal correction unit based on the first gain value and the second gain value.   
   
   
       13 . The optical disc device according to  claim 8 , further comprising:
 a spherical aberration correction unit operable to correct a spherical aberration of the spot of the light beam during at least one of the operation of moving the spot of the light beam toward the optical disc and the operation of moving the spot of the light beam away from the optical disc performed by the focus drive unit when the spot of the light beam passes through each of all the information surfaces of the optical disc, wherein the spherical aberration correction is performed in parallel with the operation performed by the focus drive unit in a manner to reduce the spherical aberration of the spot of the light beam to substantially zero on a selected information surface through which the spot of the light beam passes.   
   
   
       14 . The optical disc device according to  claim 8 , further comprising:
 a spherical aberration correction unit operable to correct a spherical aberration of the spot of the light beam on a selected information surface of the optical disc; and   an each-layer signal ratio calculation unit operable to perform processing of first activating an operation of the spherical aberration correction unit on a selected information surface of the optical disc and then activating an operation of obtaining the predetermined gain value performed by the signal ratio calculation unit during at least one of the operation of moving the spot of the light beam toward the optical disc and the operation of moving the spot of the light beam away from the optical disc performed by the focus drive unit, wherein the each-layer signal ratio calculation unit performs the processing for each of all the information surfaces of the optical disc.   
   
   
       15 . The optical disc device according to  claim 1  that records and/or reads on an optical disc having a plurality of information surfaces, the device further comprising:
 a plurality-of-information-surface signal ratio calculation unit operable to calculate, as the predetermined gain value to be used by the signal correction unit, a common gain value that is used commonly for the plurality of information surfaces of the optical disc,   wherein the signal ratio calculation unit obtains a plurality of predetermined gain values for the plurality of information surfaces, and   the plurality-of-information-surface signal ratio calculation unit obtains the common gain value based on the plurality of predetermined gain values for the plurality of information surfaces that are obtained by the signal ratio calculation unit.   
   
   
       16 . The optical disc device according to  claim 15 , further comprising:
 a focus control unit operable to control the spot of the light beam to be positioned on an information surface of the optical disc in accordance with a signal output from the focus error signal generation unit; and   a focusing unit operable to move the spot of the light beam in a direction perpendicular to the disc surface of the optical disc using the focus drive unit, and activate a control operation performed by the focus control unit when the spot of the light beam is positioned on a selected information surface of the optical disc,   wherein the plurality-of-information-surface signal ratio calculation unit obtains the common gain value based on an output from the measurement unit at least once before the focusing unit activates the control operation performed by the focus control unit.   
   
   
       17 . A focus error signal adjusting method used in an optical disc device that records and/or reads on an optical disc having an information surface and includes
 an illumination unit operable to emit a light beam to the optical disc,   a converging unit operable to converge the light beam emitted from the illumination unit,   a focus drive unit operable to drive the converging unit in a manner to move a spot of the light beam that has been converged by the converging unit in a direction perpendicular to a disc surface of the optical disc, and   a light receiving unit including a plurality of divisional detectors, and operable to receive reflected light from the optical disc using the plurality of divisional detectors and obtain, as a positive FE signal and a negative FE signal, an electric signal corresponding to an amount of the received light,   the method comprising:
 measuring a signal level of each of the positive FE signal and the negative FE signal obtained by the light receiving unit; 
   correcting the signal level of at least one of the positive FE signal and the negative FE signal by multiplying the at least one of the positive FE signal and the negative FE signal by a predetermined gain value;   generating a focus error signal based on an output from the signal correction unit, and outputting the generated focus error signal; and   obtaining, based on an output in the measurement step, the predetermined gain value by which the at least one of the positive FE signal and the negative FE signal is to be multiplied in a manner that the predetermined gain value causes an absolute value of a local maximum value of the focus error signal to be equal to an absolute value of a local minimum value of the focus error signal,   wherein in the signal correction step, the signal level of the at least one of the positive FE signal and the negative FE signal is corrected based on the predetermined gain value obtained in the signal ratio calculation step.   
   
   
       18 . A program enabling a computer to implement a focus error signal adjusting method used in an optical disc device that records and/or reads on an optical disc having an information surface and includes
 an illumination unit operable to emit a light beam to the optical disc,   a converging unit operable to converge the light beam emitted from the illumination unit,   a focus drive unit operable to drive the converging unit in a manner to move a spot of the light beam that has been converged by the converging unit in a direction perpendicular to a disc surface of the optical disc, and   a light receiving unit including a plurality of divisional detectors, and operable to receive reflected light from the optical disc using the plurality of divisional detectors and obtain, as a positive FE signal and a negative FE signal, an electric signal corresponding to an amount of the received light,   the method comprising:
 measuring a signal level of each of the positive FE signal and the negative FE signal obtained by the light receiving unit; 
   correcting the signal level of at least one of the positive FE signal and the negative FE signal by multiplying the at least one of the positive FE signal and the negative FE signal by a predetermined gain value;   generating a focus error signal based on an output from the signal correction unit, and outputting the generated focus error signal; and   obtaining, based on an output in the measurement step, the predetermined gain value by which the at least one of the positive FE signal and the negative FE signal is to be multiplied in a manner that the predetermined gain value causes an absolute value of a local maximum value of the focus error signal to be equal to an absolute value of a local minimum value of the focus error signal,   wherein in the signal correction step, the signal level of the at least one of the positive FE signal and the negative FE signal is corrected based on the predetermined gain value obtained in the signal ratio calculation step.   
   
   
       19 . An integrated circuit used in an optical disc device that records and/or reads on an optical disc having an information surface and includes
 an illumination unit operable to emit a light beam to the optical disc,   a converging unit operable to converge the light beam emitted from the illumination unit,   a focus drive unit operable to drive the converging unit in a manner to move a spot of the light beam that has been converged by the converging unit in a direction perpendicular to a disc surface of the optical disc, and   a light receiving unit including a plurality of divisional detectors, and operable to receive reflected light from the optical disc using the plurality of divisional detectors and obtain, as a positive FE signal and a negative FE signal, an electric signal corresponding to an amount of the received light,   the integrated circuit comprising:
 a measurement unit operable to measure a signal level of each of the positive FE signal and the negative FE signal obtained by the light receiving unit; 
   a signal correction unit operable to correct the signal level of at least one of the positive FE signal and the negative FE signal by multiplying the at least one of the positive FE signal and the negative FE signal by a predetermined gain value;   a focus error signal generation unit operable to generate a focus error signal based on an output from the signal correction unit, and output the generated focus error signal; and   a signal ratio calculation unit operable to obtain, based on an output from the measurement unit, the predetermined gain value by which the at least one of the positive FE signal and the negative FE signal is to be multiplied in a manner that the predetermined gain value causes an absolute value of a local maximum value of the focus error signal to be equal to an absolute value of a local minimum value of the focus error signal,   wherein the signal correction unit corrects the signal level of the at least one of the positive FE signal and the negative FE signal based on the predetermined gain value obtained by the signal ratio calculation unit.